An integrated fan coil refers to an air handling system which combines in one appliance the typical functions of a hydronic or direct exchange air handler and the typical functions of an HRV/ERV device. A typical direct exchange air handler includes a forced air furnace circulating heated or air conditioned air to an interior space via a duct or direct grille return system. A typical HRV or ERV device brings fresh air into an interior space from outdoors via a duct system with a heat exchange core, and expels exhaust and stale air from that same interior space via the heat exchange core, which transfers sensible and latent energy from the exhaust air to the fresh air. Typically, the HRV/ERV core, helps control the relative humidity of the interior space, and recovers energy from the exhaust air stream.
Conventional HRV devices, such as those disclosed in U.S. Pat. No. 4,653,574 issued Mar. 31, 1987 to L.B. White Company, Inc; U.S. Pat. No. 5,257,736 issued Nov. 2, 1993 to Donald Roy; U.S. Pat. No. 5,855,320 issued Jan. 5, 1999 in the name of Nutech Energy Systems Inc.; and U.S. Pat. No. 6,169,849 issued Jan. 2, 2001 to Olsberg Hermann Everken GmbH, provide a heat exchanging core to enable the transfer of heat from exhaust air to intake air. Unfortunately, prior art HRV systems do not, without drawbacks, solve the problem of heat exchange cores becoming too cold and frosting over.
A simple conventional defrosting system is to shut down the fresh air input fan and exhaust interior air through the heat exchange core. Unfortunately, fan shut-down defrost systems cause negative pressurization of the interior space, as they exhaust air through the HRV/ERV core to thaw the core out, without introducing fresh air into the interior space because the fresh air fan is “shut down” during defrost cycles. Moreover, during defrost cycles, fan shut-down HRV/ERV systems expel heat from the interior space without passing any of that heat on to incoming fresh air, since fresh air is not coming into the building when the fresh air fan is shut off, resulting in heat energy loss. Another short-coming of fan shut-down defrost systems is that they take longer to defrost the HRV/ERV core than other defrost systems because fan shut-down systems provide warm air to only one side of the core.
There is no negative pressurization of the interior space and its associated heat energy loss, no need to locate or run special ductwork, nor any special consideration needed for unit location (in terms of defrost performance), all typical disadvantages of “5th port” defrost systems.
Conventional 5th port defrost systems address the issue of feeding defrost air to both sides of the HRV/ERV core, thereby performing their function faster than fan shut-down defrost systems; however, they still create negative pressurization of the interior space resulting in energy losses. Another disadvantage of 5th port defrost systems is that they require an extra duct, which is used for defrost purposes, to be run between the unit and the interior space. As the space in building design for mechanical ventilation systems is usually minimal, adding a 5th port can present major space and aesthetic issues, not to mention added costs of running the duct for the 5th port. Alternatively, the HRV/ERV could be located in a room to draw defrost air into the unit directly. While this method of installation eliminates the need for special ductwork, care must be given in unit location: the room in which the unit is located must be heated and this room must not contain any source of noxious odours or airborne chemicals.
Re-circulation defrost systems address the efficiency, space, aesthetic and cost shortcomings of fan shut-down and 5th port defrost systems; however, recirculation defrost systems re-circulate stale and exhaust air through the HRV/ERV core, thus delivering, stale and perhaps smelly air to the interior space during defrost cycles, adversely affecting the level of comfort experienced by occupants of the interior space.
An object of the present invention is to overcome the shortcomings of the prior art by providing a HRV or ERV defrosting unit, which doesn't require negative depressurization of the interior space, an external 5th port, or re-circulation of exhaust air into the interior space.